Application of energy with cooling elements for skin treatment

ABSTRACT

A system and method for simultaneously heating a plurality of discrete skin volumes to a coagulation temperature. The system comprises an applicator containing an electrode having a plurality of spaced apart protruding conducting elements configured to contact the skin surface at a plurality of discrete locations. A controller applies a voltage to the electrode so as to simultaneously heat a plurality of skin volumes to a coagulation temperature when the applicator is applied to the skin surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is being filed under 35 USC 111 and is a continuationof the following U.S. patent application Ser. No. 13/925,832 filed onJun. 25, 2013, which is a continuation of Ser. No. 12/876,765 filed onSep. 7, 2010 and issued as U.S. Pat. No. 8,579,896 on Nov. 12, 2013,which is a continuation of Ser. No. 12/702,647 filed on Feb. 9, 2010,which is a continuation of Ser. No. 12/702,723 filed on Feb. 9, 2010 andwhich is now abandoned, which is a continuation of Ser. No. 10/931,271filed on Sep. 1, 2004 now abandoned; and Ser. No. 13/028,216 filed onFeb. 15, 2011, which is a continuation of Ser. No. 10/931,271 filed onSep. 1, 2004 and is now abandoned. Each of these applications isincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to methods and systems for skin treatment.

BACKGROUND OF THE INVENTION

Directed damage of the skin is used to stimulate regrowth of collagenand to improve skin appearance. A well known method of directed damageis ablating the epidermis using laser radiation having wavelengthsstrongly absorbed by water so as to heat the water to above boilingtemperature. Typical lasers used for epidermis ablation are CO.sub.2 andEr:YAG lasers. Ablating the epidermis using RF (radiofrequency) currentis described in U.S. Pat. No. 6,309,387. This treatment significantlyreduces wrinkles and improves the skin appearance. The maindisadvantages of skin resurfacing are the long healing period that canbe over a month long and the high risk of dischromia. Thesedisadvantages have reduced the popularity of ablative skin resurfacingin recent years.

Non-ablative skin resurfacing is based on heating of the dermis to asub-necrotic temperature with simultaneous cooling of the skin surface.U.S. Pat. No. 5,810,801 describes penetrating the dermis with infraredlaser radiation with dynamic cooling of the skin surface using a cryogenspray.

Wrinkles are created in skin due to the breakage of collagen fibers andto the penetration of fat into the dermal structure. Thus, destroyingadipose cells and structure, can improve the surface structure. However,most wrinkle treatment methods target the collagen and do not have asignificant effect on deep wrinkles Radio frequency (RF) energy has beenused for the treatment of the epidermal and dermal layers of the skin.For example, U.S. Pat. No. 6,749,626 describes use of RF for collagenformation in dermis. This patent describes a method for collagen scarformation. U.S. Pat. Nos. 6,470,216, 6,438,424, 6,430,446, and 6,461,378disclose methods and apparatuses for affecting the collagen matrix usingRF with special electrode structures together with cooling and smoothingof the skin surface. U.S. Pat. Nos. 6,453,202, 6,405,090, 6,381,497,6,311,090, 5,871,524, and 6,452,912 describe methods and apparatuses fordelivering RF energy to the skin using a membrane structure. U.S. Pat.Nos. 6,453,202 and 6,425,912 describe methods and apparatuses fordelivering RF energy and creating a reverse temperature gradient on theskin surface. Although a non-ablative treatment is much safer and doesnot scar the skin tissue, the results of non-ablative treatments areless satisfactory.

A method described in U.S. patent application No. 20030216719 attemptsto maintain the efficiency of ablative treatment with a shorter healingtime and a lower risk of adverse effects. The device described in thatpatent coagulates discrete regions of the skin where the regions have adiameter of tens of micrometers and the distance between the regions islarger than the regions themselves. This treatment provides skin healingwithin a few days but the results are very superficial and lessspectacular than with CO.sub.2 laser treatment, even after multipletreatments.

U.S. Pat. No. 6,277,116 describes a method of applying electromagneticenergy to the skin through an array of electrodes and deliveryelectrolyte using a microporous pad.

A device for ablation of the skin stratum corneum using RF electrodes isdescribed in U.S. Pat. Nos. 6,711,435, 6,708,060, 6,611,706, and6,597,946. However, the parameters of this device are optimized for theablation of the stratum corneum so as to enhance drug penetration intothe skin, and not for thermal collagen remodeling.

SUMMARY OF THE INVENTION

The present invention provides a system and method for simultaneouslyheating skin at a plurality of discrete regions of the skin. Theinvention may be used for collagen remodeling. In accordance with theinvention RF energy is applied to the skin at a plurality of discretelocations on the skin. The RF energy is applied using an electrodehaving a plurality of spaced apart protruding conducting pins. When theelectrode is applied to the skin surface, each protruding conducting pincontacts the skin surface at a different location, so that the pluralityof pins contacts the skin at a plurality of discrete locations. An RFvoltage is then applied to the electrode so as to generate an electriccurrent in the skin that heats the skin to a coagulation temperaturesimultaneously at a plurality of discrete regions of the skin.Coagulation temperatures are typically in the range of about 60.degree.C. to about 70.degree. C.

The protruding pins may have blunt tips which do not penetrate into theskin when the electrode is applied to the skin. In this case, thediscrete regions of treated skin are located at the skin surface in theepidermis. Alternatively, the pins may have sharp tips that allow theprotruding pin to penetrate the skin into the dermis. In this way, thediscrete regions of treated skin are located in the dermis.

In another embodiment, the protruding elements are provided with sharptips that allow the elements to penetrate into the skin. Afterapplication of the RF current in the skin, the protruding elements arepressed into the skin and an electrical current is then generated thatcoagulates tissue in the vicinity of the tip of each protruding element.The mechanical properties of the skin are changed after coagulation andthe protruding elements may penetrate inside the skin without excessivepressure. A pre-pulse of RF energy can be applied to the skin in orderto soften the skin tissue so as to facilitate penetration of theprotruding elements into the skin.

The surface of the skin may be pre-cooled and/or cooled during thetreatment to avoid damage to the skin in the area between protrudingelements Skin cooling may be provided by contact cooling or by applyinga pre-cooled liquid or cryogen spray.

The invention may be used in wrinkle treatment, collagen remodeling,skin tightening, loose skin treatment, sub-cutaneous fat treatment orskin resurfacing.

Thus in its first aspect, the invention provides a system forsimultaneously heating a plurality of discrete skin volumes to acoagulation temperature, comprising:

-   -   (a) an applicator comprising an electrode having a plurality of        spaced apart protruding conducting elements configured to        contact the skin surface at a plurality of discrete locations;        and    -   (b) a controller configured to apply a voltage to the electrode        so as to simultaneously heat a plurality of skin volumes to a        coagulation temperature when the applicator is applied to the        skin surface.

In its second aspect, the invention provides a method for simultaneouslyheating a plurality of discrete skin volumes to a coagulationtemperature, comprising:

-   -   (a) applying an applicator to the skin surface, the applicator        comprising an electrode having a plurality of spaced apart        protruding conducting elements configured to contact the skin        surface at a plurality of discrete locations; and    -   (b) applying a voltage to the electrode so as to simultaneously        heat a plurality of skin volumes to a coagulation temperature.

In the case when protruding part of the electrode penetrates within theskin the size of protruding elements should be small enough to avoidsignificant damage of the skin surface. Preferable size of protrudingelements is from 10 to 200 microns and coagulation depth can be variedfrom 100 microns up to 2 mm for invasive electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, preferred embodiments will now be described, by way ofnon-limiting examples only, with reference to the accompanying drawings,in which:

FIG. 1 shows a system for treating skin simultaneously at a plurality ofdiscrete regions of skin, in accordance with the invention;

FIGS. 2A and 2 b (collectively referred to as FIG. 2 in the description)shows an applicator for use in the system of FIG. 1 with FIG. 2A showingthe applicator alone and FIG. 2B showing the applicator being applied toa target tissue area;

FIG. 3 shows a second applicator for use in the system of FIG. 1; and

FIG. 4 shows a third applicator for use in the system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a system for applying RF energy to a plurality of discreteregions of skin in accordance with the invention. The system includes anapplicator 13, to be described in detail below, configured to apply RFenergy simultaneously to a plurality of discrete regions of skin of anindividual 22. The applicator 13 is connected to a control unit 11 via acable 12. The control unit 11 includes a power source 18. The powersource 18 is connected to an RF generator 15 that is connected toelectrodes in the applicator 13 via wires in the cable 12. The controlunit 11 has an input device such as a keypad 10 that allows an operatorto input selected values of parameters of the treatment, such as thefrequency, pulse duration and intensity of the RF energy. The controlunit 11 optionally contains a processor 9 for monitoring and controllingvarious functions of the device.

FIGS. 2A and 2 b (collectively referred to as FIG. 2 in the description)shows an applicator for use in the system of FIG. 1 with FIG. 2A showingthe applicator alone and FIG. 2B showing the applicator being applied toa target tissue area. FIG. 2 shows an applicator 13 a that may be usedfor the applicator 13 in accordance with one embodiment of theinvention. The applicator 13 a comprises an electrode 1 from which aplurality of protruding conducting elements 5 extend. Each protrudingelement 5 (referred to herein as a “pin”) terminates in a tip 7 having ahigh curvature. The electrical current from the tips is much higher thanfrom flat parts 6 of the electrode. Skin volumes 4 around the tips 7(shown in FIG. 2B) are therefore heated to a much higher temperaturethan the surrounding dermis 3 and epidermis 2, so that the skin volumes4 may be heated to a coagulation temperature, while the skin temperaturein the outside the volumes 4 are not heated to a coagulationtemperature. The electrical energy is adjusted to selectively damageskin adjacent to tips so that the treatment of the skin occurssimultaneously at a plurality of discrete volumes 4. The pulse durationis preferably short enough to prevent significant heat diffusion farfrom the tips. In order to limit significant heat transfer from thetips, the pulse duration should preferably not exceed 200 ms. Theselectivity of the treatment can be improved by electrode cooling of theskin surface. Cooling also causes a more uniform heat distribution atthe tips. This can be achieved by circulating a cooling fluid throughtubes 8 in the flat regions 6 between the pins 5. The electrode 1 iscontained in a housing 10 connected to the cable 12. The cable 12electrically connects the electrode 1 with a terminal of the powersource 18. A second terminal of the power supply 18 may be connected toa ground electrode 20 via a cable 23 (See FIG. 1).

FIG. 3 shows an applicator 13 b that may be used for the applicator 13in accordance with another embodiment of the invention. The applicator13 b comprises an electrode 100 consisting of a plurality of conductingpins 101 extending from a conducting plate 102. The pins 101 areseparated by electrical insulating material 105. The applicator 13 b isused similarly as the applicator 13 a to deliver electrical current todiscrete volumes of skin 4.

The pins 5 in the applicator 13 a and the pins 101 in the applicator 13b are provided with blunt tips 7 and 107, respectively. This preventsthe pins 5 and 101 from penetrating into the skin when the electrode 13a or 13 b is applied t the skin surface. Thus, the applicators 13 a and13 b provide simultaneous non-invasive coagulation of skin regions 4.

FIG. 4 shows an applicator 13 c that may be used for the applicator 13in accordance with another embodiment of the invention. The applicator13 c is configured to be used for invasive collagen remodeling. Theapplicator 13 c includes an electrode 201 having a plurality ofprotruding conducting pins 205. The pins 205 have sharp tips 206 thatare configured to penetrate through the epidermis 202 into the dermis203 when pressed on the skin as shown in FIG. 4. The applicator 13 c isused similarly to the applicators 13 a and 13 b so that the treatment ofthe skin occurs simultaneously in a plurality of discrete skin volumes204. However, unlike the discrete volumes 4, which are located in theepidermis (see FIGS. 2 and 3), the volumes 204 are located below thesurface in the dermis 203 (FIG. 4). This reduces skin redness thatsometimes occurs when the treated regions are in the epidermis. Amaximal current density is created at the tips of the pins 205. Thesides of the protruding elements may be coated with insulating materialto avoid skin heating around the pins 205 (not shown).

The present invention can be combined with other methods of skintreatment including laser treatment. For example non-ablative collagenremodeling by laser radiation may be combined with the invasive RFheating of the skin dermis in accordance with the invention.

The preferable parameters for non-invasive skin coagulation inaccordance with the invention are as follows: [0032] Electrode sizeabove 0.3 cm; [0033] Protruding element at contact with the skin up to0.5 mm [0034] Protruding element height about 1 mm. [0035] Distancebetween protruding elements at least twice the element diameter; [0036]Current density: over 1 A/cm.sup.2; [0037] RF current pulse duration:not longer than 0.5 sec; [0038] The optimal parameters for invasive skincoagulation:

Electrode size above 0.3 cm; [0040] Pin diameter at contact with theskin not larger than 0.3 mm [0041] Pin protruding height above 1 mm.[0042] Distance between pins at least 1 mm; [0043] Current density above0.1 A/cm.sup.2; [0044] RF current pulse duration not longer than 0.5sec.

What is claimed is:
 1. A skin treatment apparatus for selectivelytreating volumes of skin tissue, comprising: a plurality of spaced apartconducting elements configured to contact a skin surface at a pluralityof discrete locations, the plurality of conducting elements beingconfigured to receive energy from a radio frequency energy generator;and a cooling element configured to cool regions between the pluralityof conducting elements so as to maintain the skin surface between theplurality of discrete locations below a coagulation temperature when theplurality of conducting elements are energized.
 2. The apparatusaccording to claim 1, wherein the cooling element comprises a coolingfluid in contact with the regions between the plurality of conductingelements.
 3. The apparatus according to claim 2, wherein the coolingelement comprises a plurality of tubes through which the cooling fluidcirculates, the plurality of tubes being located in the regions betweenthe plurality of conducting elements.
 4. The apparatus according toclaim 1, wherein the cooling element is configured to apply a cryogenspray to the skin surface in the regions between the plurality ofconducting elements.
 5. The apparatus according to claim 1, wherein theplurality of conducting elements are terminated by sharp tips that areconfigured to penetrate the skin surface at the plurality of discretelocations.
 6. The apparatus according to claim 1, wherein the pluralityof conducting elements are terminated by blunt tips that are notconfigured to penetrate into the skin surface at the plurality ofdiscrete locations.
 7. An applicator for selective treatment of discreteskin volumes, said applicator comprising: a plurality of conductingelements configured to receive energy from a radio frequency energygenerator and to contact a skin surface at a plurality of discretelocations to apply the received energy to the plurality of discretelocations of the skin surface, the plurality of conducting elementsextending from a flat surface and being spaced apart from one anotherwith regions of the flat surface interposed between the plurality ofconducting elements; and a cooling element configured to cool theregions of the flat surface between the plurality of conducting elementsso as to maintain the skin surface between the plurality of discretelocations below a coagulation temperature when the plurality ofconducting elements are energized and brought into contact with the skinsurface.
 8. The applicator according to claim 7, wherein the coolingelement comprises a cooling fluid in contact with the regions of theflat surface interposed between the plurality of conducting elements. 9.The applicator according to claim 8, wherein the cooling elementcomprises a plurality of tubes through which the cooling fluidcirculates, the plurality of tubes being located in the regions of theflat surface interposed between the plurality of conducting elements.10. The applicator according to claim 7, wherein the cooling element isconfigured to apply a cryogen spray to the skin surface in the regionsof the flat surface interposed between the plurality of conductingelements.
 11. The applicator according to claim 7, wherein the pluralityof conducting elements are terminated by sharp tips that are configuredto penetrate the skin surface at the plurality of discrete locations.12. The applicator according to claim 7, wherein the plurality ofconducting elements are terminated by blunt tips that are not configuredto penetrate into the skin surface at the plurality of discretelocations.
 13. The applicator according to claim 7, wherein theplurality of conducting elements are configured to apply the receivedenergy to the plurality of discrete locations of the skin surface with apulse duration of less than 200 ms.